diff -r 4b2fdd4dd700 Objects/fileobject.c
--- a/Objects/fileobject.c	Tue Jun 11 15:00:21 2013 -0700
+++ b/Objects/fileobject.c	Tue Jun 11 18:57:53 2013 -0700
@@ -121,9 +121,15 @@
 {
 #if defined(HAVE_FSTAT) && defined(S_IFDIR) && defined(EISDIR)
     struct stat buf;
+    int fd;
+
     if (f->f_fp == NULL)
         return f;
-    if (fstat(fileno(f->f_fp), &buf) == 0 &&
+
+    if((fd = fileno(f->f_fp)) < 0)
+        return f;
+
+    if (fstat(fd, &buf) == 0 &&
         S_ISDIR(buf.st_mode)) {
         char *msg = strerror(EISDIR);
         PyObject *exc = PyObject_CallFunction(PyExc_IOError, "(isO)",